Mr Mangold, a senior investigative journalist with the BBC's Panorama programme for nearly 30 years and a close friend of 59-year-old Dr Kelly, was driven up to the church in a silver Jaguar at 12.45pm.

He paused briefly at the gates of the churchyard before making his way into the 13th century chapel.

Mr Mangold collaborated with Dr Kelly while writing a book and making a documentary about chemical and biological weapons.

Mounted police patrolled fields surrounding St Mary's while a sniffer dog was brought in to carry out a sweep of the church itself.

At around noon the Union Flag was hoisted to half mast on a flag pole in the churchyard.

Inquiry opened

Visible just over a mile away from the church is Harrowdown Hill, where Dr Kelly's body was found with a slashed left wrist and an open packet of painkillers on July 18.

The order of service was expected to feature elements of the Baha'i religion, which 59-year-old Dr Kelly converted to four years ago while studying in the US. His family is said to have chosen Baha'i prayers from a selection made by followers at his local Baha'i centre in Abingdon.

Lord Hutton opened his inquiry into death of Dr Kelly, who was named as the mole for BBC reports that Downing Street "sexed up" its Iraq dossier, last week.

An inquest into Dr Kelly's death, opened and adjourned on July 21 at Oxfordshire Coroner's Court, found the scientist died from an "incised wound" to the left wrist.

Coroner Nicholas Gardiner released Dr Kelly's body to his family on July 25 but refused to give the results of toxicology tests until a full inquest.